1. Field of the Invention
This invention relates to a non-aqueous electrolyte cell employing a cell device obtained on layering and coiling a strip-shaped cathode material and a strip-shaped anode material together. More particularly, it relates to improvement in a cell device.
2. Description of Related Art
Nowadays, in keeping up with the recent marked progress in the electronic equipment, researches into re-chargeable cells, as power sources usable conveniently and economically for prolonged time, are underway. Representative of the cells are lead accumulators, alkali accumulators and non-aqueous electrolyte cells.
Of the above cells, lithium ion secondary cells, as non-aqueous electrolyte cells, have such merits as high output and high energy density.
The lithium ion secondary cells are made up of a cathode and an anode, including active materials capable of reversibly doping/dedoping lithium ions, and a non-aqueous electrolyte. The charging reaction of the lithium ion cell proceeds as lithium ions are deintercalated into an electrolyte solution at the cathode and are intercalated into the anode active material. In discharging, reaction opposite to that of the charging reaction proceeds, such that lithium ions are interecalated at the cathode. That is, charging/discharging is repeated as the reaction of entrance/exiting of lithium ions from the cathode into the anode active material and from the anode active material occurs repeatedly.
Currently, LiCoO2, LiNiO2 or LiMn2O4 are used as the cathode active material of the lithium ion secondary cell because these materials exhibit a high energy density and a high voltage.
However, if the aforementioned active material is used, both the cathode material and the anode material undergo volumetric expansion and contraction, during charging and discharging, respectively, thus producing marked volumetric changes. Thus, if, in case of a cell accommodating the electrolyte solution and the cell device in an iron cell can, the cathode and anode materials are layered and coiled together to form a cell device, the cathode and anode materials are coiled to too small an inner diameter, the layers of the cathode active material or the anode active material in the vicinity of the center of the coil tend to be deteriorated, peeled of or detached due to the volumetric changes of the cell device during charging/discharging, thus causing internal shorting or deteriorating the volumetric upkeep ratio to render it impossible to realize satisfactory cyclic characteristics.
Moreover, depending on the structure of the cell device, specifically the value of the ratio of the inner diameter d to the outer diameter D, or d/D, the amount of the active material introduced into the cell device cannot be counterbalanced with respect to the amount of the electrolyte solution to render it impossible to realize a high discharge capacity.